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Evidence shows cannabis extract can reduce epileptic seizures

Cannabidiol clinical trial indicates lower seizure rates among children with Dravet syndrome, a rare form of epilepsy. Andrew Masterson reports.

Clinical data supports the mass of anedotal evidence that the cannabis extract cannabidiol can reduce seizures for sufferers of certain kinds of epilepsy.

Ashley Rosenberg / EyeEm / Getty

There have long been anecdotally supported suggestions that cannabidiol, a cannabis derivative, can reduce seizures in children suffering from a rare form of epilepsy. Now some clinical evidence has arrived to back them up.

A team led by neurologist Orrin Devinsky from New York University’s Langone Medical Centre report in the New England Journal of Medicine that the derivative can substantially ameliorate seizures caused by Dravet syndrome, an uncommon but severe form of epilepsy.

Devinsky’s team enlisted 120 children with Dravet syndrome, aged between two and 18, at 23 sites across the US and Europe. Half of the participants were given a daily dose of cannabidiol (CBD), a non-psychoactive marijuana extract, while the rest received a placebo.

The trial ran for 14 weeks, and all the children continued to receive previously prescribed medications for the duration.

The results – which were first presented in April at an American Academy of Neuroscience conference in Boston – found that in the CBD group the median number of severe seizures experienced each month fell from about 12 to six, while three patients experienced none at all. All up, seizure reduction was 39%.

In the control group, seizures reduced by about one a month.

The cannabidiol product used was made by UK company GW Pharmaceuticals, which also funded the research.

The idea that CBD could have a dampening effect on epilepsy was explored as early as 1980, when a team from Brazil tested it on a small sample of epileptic patients and reported (in the journal Pharmacology) significant reductions in seizure events.

For much of the latter part of the 20th century, however, research into the possible medicinal properties of marijuana was severely curtailed, because cultivation and possession of the source plant was illegal in most countries.

Relaxation of regulations in Europe and North America in recent years has spurred considerable investment in both research and commercialisation of cannabis-derived products.

Pharmaceutical interests such as GW are eager to fund clinical trials, because without peer-reviewed evidence they are unable to market their products as anything other than health supplements. The race is on, therefore, to find quantitative results to back up anecdotal testimony.

"Cannabidiol should not be viewed as a panacea for epilepsy,” says Devinsky, “but for patients with especially severe forms who have not responded to numerous medications these results provide hope that we may soon have another treatment option."